We will analyze the transcription unit sizes for adult, murine hemoglobin alpha and beta chain genes by UV mapping. This technique bypasses the need for isolating the primary transcript, which would be impossible if processing were to start before the completion of the RNA chain. Induce Friend's leukemia virus transformed cells (GM 86) with 2% DMSO, label nuclear RNA with 3H-uridine for 20-40 min immediately following UV irradiation at different doses. Isolate the RNA and quantify the fraction of mRNA homologous to the Hb alpha and beta messenger sequences. RNA will be quantified by hybridization to denatured, filter-bound plasmid DNA containing the murine alpha and beta mRNA sequences (clones obtained from the laboratory of Charles Weissmann). UV sensitivities will be converted to DNA lengths using rDNA genes and specific mRNA size classes as internal standards.